Lecture 14: Inhalational Anesthesia Flashcards
What is the significance of switching from ether to desflurane as an inhalational anesthetic agent?
Putting fluorine on the diethyl ether = less flammable
What are the 4 benefits of halogenated volatile agents?
- Anesthetic POTENCY
- SOLUBILITY in fat and blood
- Degree of noxious character/PUNGENCY
- CHEAPER cost per mL
What are the key characteristics of nitrous oxide?
- Very rapid onset & offset
- Useful for inhalational sedation (dental procedure)
- Not a potent complete anesthetic alone
- Used in combination with other agents such as opioids for general anesthesia
- Overall use in anesthesia decreasing due to known side-effects
What are the components of general anesthesia?
- Asleep (hypnosis)
- Forgetful (amnesia)
- Comfortable (analgesia)
- Still (immobility/muscle relaxation/Akinesia)
- Unresponsive (blunting of autonomic reflexes)
- tachycardia, hypertension, bradycardia
What are some goals of anesthesia?
NOT arousable
Anesthetic state is readily induced and readily reversible
Fill the motherfucking lungsss in inhalational anesthesia
What are the cerebral effects of anesthesia?
Increase synchrony of brain activity (less entropy)
Anesthetics decrease metabolism
What are the key characteristics of delivery of anesthetic gas?
- Liquid anesthetic agent is vaporized in controlled fashion
- Gas inhaled via breathing circuit to fill lungs
- Uptake into blood and distributed
i. brain, liver, kidney (Vessel Rich Groups)
ii. Fat (lowest % cardiac blood flow)
iii. Muscle (intermediate % blood flow) - Eliminated by pulmonary ventilation
- No metabolic breakdown of inhaled agents
What are the vessel rich groups?
i. brain
ii. liver
iii. kidney
Where are anesthetics least soluble?
In the brain
Where are the anesthetics most soluble? Significance?
In fat
Significance is that anesthetics accumulates in fat
We want to have the LEAST soluble anesthetic so we can reverse the effects most quickly
Desflurane = least soluble = most easily reversible = most expensive
What are the characteristics of a LESS soluble anesthetic?
- Less potent (but can keep gas in lungs)
- FASTER onset/faster offset
- Less accumulation in tissue/fat
What fluoroether has the lowest solubility? Highest solubility?
Desflurane = lowest solubility = least potent = fastest onset/offset Isoflurane = most soluble
What is the organizing principle of inhalational anesthesia?
We are trying to fill the lung with gas
So if the gas is soluble (i.e is readily diffusible into blood), then it is taken out of lung even faster, which runs counter to your goal
That’s why desflurane is most effective
What are the CNS effects of anesthetics?
- produce unconciousnes
- DECREASE cerebral METABOLIC activity
- INCREASE cerebral BLOOD FLOW
- Impair cerebral autoregulation
- Impair memory formation
- Block movement in response to stimulus (at level of spinal cord)
- Dose-dependent changes in EEG
What are the pulmonary/respiratory effects of inhaled agents?
- Profound bronchoDILATION (open airways)
- Increase respiratory rate
- Decrease tidal volume (volume of a regular breath)
- Decrease reflexes to maintain ventilation/oxygenation
- Decrease ventilator response to low blood O2
- Decrease ventilator response to high blood CO2
What are the cardiovascular effects of inhaled agents?
- Dilate vessels
- DECREASE BP
- redistribute blood from core to periphery
- Impair autonomic reflexes to maintain blood pressure
- Impair contractile strength of heart muscle
What is the minimum alveolar concentration (MAC)? Significance?
The minimum alveolar concentration of inhaled agents at which 50% of patients will NOT move in response to surgical incision
Significance is that anesthetic efficacy is defined by what’s in the lung
MAC is different for each inhaled volatile agent
Example: sevoflurane = 2.2% and isoflurane = 1.0%
What are the key characteristics of MAC?
- MAC is NOT a physical property of anesthetic agent
- MAC influenced by variety of factors
- % of anesthetic gas (MAC fraction) of total gas exchanged in lungs is measured continuously via inspired/expired gas %
What factors determines complete anesthesia for patients?
-intensity and type of surgery
-age and medical condition
(MAC lowers as you age)
-concurrent use of other anesthetics in addition to anesthetic gas (opiods, muscle relaxants)
What are problems with inhaled anesthetics?
- Nausea and Vomiting
- Respiratory depression
- Cardiovascular collapse
- inhibition of uterine contraction
What is the mechanism of inhaled anesthetics?
We don’t know!
Because we don’t have definition of consciousness
What is the current theory of inhalational anesthetic MOA?
Allosteric binding of inhaled agents to specific binding sites – protein/anesthetic/lipid complex alters function
GABA_A is the key receptor and neurotransmitter in anesthetic effects
Desflurane can bind to GABA_A
What are the sites of action for anesthesia?
Cortex
Thalamus
Brainstem
Spinal cord
What is the central neurotransmitter that mediates the effects of anesthetic effects?
GABA
Why can anesthesia have adverse effect in children?
There is a LOT of INFLAMMATION that takes place when you undergo anesthesia + surgery
-so it could be the inflammation that leads to impaired synapse formation and increase likelihood of neurodegeneration
Bottom line: we don’t know what the detrimental of effects of anesthesia are, if any
MAC of an inhaled volatile anesthetic is defined as
Minimum Alveolar Concentration that prevents MOVEMENT at surgical incision in 50% of patients
During mask induction of anesthesia with a lipid soluble inhaled anesthetic gas the greatest amount of anesthetic is delivered to the
Adipose tissue
What is one major effect of anesthetic agents on pulmonary function?
Bronchodilation
